Methods for producing in-situ grooves in chemical mechanical planarization (CMP) pads, and novel CMP pad designs

ABSTRACT

Methods for producing in-situ grooves in CMP pads are provided. In general, the methods for producing in-situ grooves comprise the steps of patterning a silicone lining, placing the silicone lining in, or on, a mold, adding CMP pad material to the silicone lining, and allowing the CMP pad to solidify. CMP pads comprising novel groove designs are also described. For example, described here are CMP pads comprising concentric circular grooves and axially curved grooves, reverse logarithmic grooves, overlapping circular grooves, lassajous groves, double spiral grooves, and multiply overlapping axially curved grooves. The CMP pads may be made from polyurethane, and the grooves produced therein may be made by a method from the group consisting of silicone lining, laser writing, water jet cutting, 3-D printing, thermoforming, vacuum forming, micro-contact printing, hot stamping, and mixtures thereof.

FIELD

In general, the methods and designs described here are in the field ofpolishing pads for Chemical Mechanical Planarization (CMP). Moreparticularly, the methods and designs described here are related toin-situ grooves for CMP pads and novel CMP pad designs.

BACKGROUND

In general, CMP is used to planarize individual layers (e.g., dielectricor metal layers) during integrated circuit (IC) fabrication on asemiconductor wafer. CMP removes undesirable topographical features ofthe IC on the wafer. For example, CMP removes metal deposits subsequentto damascene processes, and excess oxide from shallow trench isolationsteps. Similarly, CMP may also be used to planarize inter-metaldielectrics (IMD), or devices with complex architecture, such assystem-on-a-chip (SoC) designs and vertical gate structures (e.g.,FinFET) with varying pattern density.

CMP utilizes a reactive liquid medium, commonly referred to as a slurry,and a polishing pad to provide chemical and mechanical control toachieve planarity. Either the liquid or the polishing pad may containnano-size inorganic particles to enhance chemical reactivity and/ormechanical activity of the CMP process. The pad is typically made of arigid, micro-porous polyurethane material capable of performing severalfunctions including slurry transport, distribution of applied pressureacross a wafer, and removal of reacted products. During CMP, thechemical interaction of the slurry forms a chemically modified layer atthe polishing surface. Simultaneously, the abrasives in the slurrymechanically interact with the chemically modified layer, resulting inmaterial removal. The material removal rate in a CMP process is relatedto slurry abrasive concentration and the average coefficient of friction(f) in the pad/slurry/wafer interfacial region. The extent of normal &shear forces during CMP and f typically depends on pad tribology. Recentstudies indicate that pad material compliance, pad contact area, and theextent of lubricity of the system play roles during CMP processes. See,e.g, A. Philiposian and S. Olsen, Jpn. J. Appl. Phys., vol. 42, pp6371-63791; Chemical-Mechanical Planarization of Semiconductors, M. R.Oliver (Ed.), Springer Series in Material Science, vol. 69, 2004; and S.Olsen, M.S. Thesis, University of Arizona, Tuscon, Ariz., 2002.

An effective CMP process not only provides a high polishing rate, butalso a finished (e.g., lacking small-scale roughness) and flat (e.g.,lacking in large-scale topography) substrate surface. The polishingrate, finish, and flatness are thought to be governed by the pad &slurry combination, pad/wafer relative velocity, and the applied normalforce pressing the substrate against the pad.

Two commonly occurring CMP non-uniformities are edge effects and centerslow effects. Edge effects occur when the substrate edge and substratecenter are polished at different rates. Center slow effects occur whenthere is under-polishing at the center of the substrate. Thesenon-uniform polishing effects reduce overall flatness.

Another commonly observed problem relates to slurry transport anddistribution. In the past, polishing pads had perforations. Theseperforations, when filled, distributed slurry when the pad wascompressed. See, e.g., J. Levert et al, Proc. Of the InternationalTribology Conf., Yokohoma, 1995. This method was ineffective becausethere was no way to directly channel the excess slurry to where it wasmost needed (i.e., at the wafer surface). Currently, macro-texturing ofpads is typically done through ex-situ pad surface groove design. See,e.g., U.S. Pat. Nos. 5,842,910; 5,921,855; 5,690,540; and T. K. Doy etal, J. of Electrochem. Soc., vol. 151, no. 3, G196-G199, 2004. Suchdesigns include, circular grooves (e.g., concentric grooves referred toas “K-grooves”) and cross-hatched patterns (e.g., X-Y, hexagons,triangles, etc.). The groove profile may also be rectangular with ‘V-’,‘U-’ or saw-tooth shaped cross sections.

SUMMARY

Methods for producing in-situ grooves in CMP pads, and novel groovedesigns are described. In general, the methods for producing in-situgrooves comprise the steps of patterning a silicone lining, placing thesilicone lining in, or on, a mold, adding CMP pad material to thesilicone lining, and allowing the CMP pad to solidify. In somevariations, the silicone lining is made from a silicone elastomer, andin some variations, patterning the silicone lining comprises the step ofpatterning the silicone lining using lithography or embossing. Themethods of producing in-situ grooves may further comprise the step ofadhering the silicone lining to the mold, for example, using glue, tape,clamps, pressure fitting techniques, or mixtures thereof.

In some variations, the mold is metallic. For example, the mold may bemade from a material selected from the group consisting of aluminum,steel, ultramold material, and mixtures thereof. In some variations, themold is patterned, in addition to the patterning of the silicone lining(i.e, a combination of patterning is used). In some variations, the CMPpad material comprises a thermoplastic material. In other variations,the CMP pad material comprises a thermoset material. In some variations,the CMP pad material is polyurethane.

CMP pads comprising novel groove designs are also described. Forexample, described here are CMP pads comprising concentric circulargrooves and axially curved grooves. In some variations, the concentriccircular grooves are spaced apart in sets. In other variations, theaxially curved grooves are overlapping. In yet other variations, theaxially curved grooves are discontinuous. The concentric circulargrooves and the axially curved grooves may also intersect.

CMP pads comprising reverse logarithmic grooves, overlapping circulargrooves, lassajous groves, double spiral grooves, and multiplyoverlapping axially curved grooves are also described. In somevariations, the overlapping circular grooves are off-center. The CMPpads may be made from polyurethane, and the grooves produced therein maybe made by a method from the group consisting of silicone lining, laserwriting, water jet cutting, 3-D printing, thermoforming, vacuum forming,micro-contact printing, hot stamping, and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B provide a schematic of the impact of grooving on thehydrodynamic pressure (P) generated around the pad/wafer region.

FIG. 2 provides a cross-sectional view of how the silicone lining methoddescribed here may be used to produce in-situ grooves.

FIGS. 3A-3I provide illustrations of suitable groove designs asdescribed herein.

DETAILED DESCRIPTION

Described here are methods for in-situ CMP grooving, and novel groovedesigns. Grooves in CMP pads are thought to prevent hydroplaning of thewafer being polished across the surface of the pad; to help providedistribution of the slurry across the pad surface; to help ensure thatsufficient slurry reaches the interior of the wafer; to help controllocalized stiffness and compliance of the pad in order to controlpolishing uniformity and minimize edge effects; and to provide channelsfor the removal of polishing debris from the pad surface in order toreduce defectivity. FIGS. 1A and 1B provide a schematic representationof the impact of grooving on the hydrodynamic pressure generated aroundthe pad/wafer region. For example, FIG. 1A, depicts a wafer pressureprofile (indicated by the diagonally striped triangular regions) when anon-grooved polishing pad is used. FIG. 1B illustrates how the pressurearound the periphery of the wafer is released along the grooves. Thatis, the grooves conform to the pressure generated at every groove pitchand, help provide uniform slurry distribution along the wafer/padregion.

Methods for In-Situ Grooving

In general, any suitable method of producing in-situ grooves on a CMPpad may be used. Unlike the current methods of ex-situ grooving, whichare mainly mechanical in nature, the in-situ methods described here mayhave several advantages. For example, the methods of in-situ groovingdescribed here will typically be less expensive, take less time, andrequire less manufacturing steps. In addition, the methods describedhere are typically more useful in achieving complex groove designs.Lastly, the in-situ methods described here are typically able to produceCMP pads having better tolerances (e.g., better groove depth, etc.).

In one variation, the methods for in-situ grooving comprise the use of asilicone lining placed inside a mold. The mold may be made of anysuitable metal. For example, the mold may be metallic, made fromaluminum, steel, ultramold materials (e.g., a metal/metal alloy having“ultra” smooth edges and “ultra” high tolerances for molding finerfeatures), mixtures thereof, and the like. The mold may be any suitabledimension, and the dimension of the mold is typically dependent upon thedimension of the CMP pad to be produced. The pad dimensions, in turn,are typically dependent upon the size of the wafer to be polished. Forexample, illustrative dimensions for CMP pads for polishing a 4, 6, 8,or 12 inch wafer may be 12, 20.5, 24.6, or 30.5 inches respectively.

The silicone lining is typically made of a silicone elastomer, or asilicone polymer, but any suitable silicone lining may be used. Thesilicone lining is then typically embossed or etched with a pattern,which is complementary to the desired groove pattern or design. Thelining is then glued or otherwise adhered to, or retained in, the mold.It should be noted that the lining may also be placed in the mold priorto it being patterned. The use of lithographic techniques to etchpatterns into the silicone lining may help provide better accuracy ingroove size. See, e.g., C. Dekker, Steriolithography tooling forsilicone molding, Advanced Materials & Processes, vol. 161 (1), pp59-61,January 2003; and D. Smock, Modern Plastics, vol. 75(4), pp 64-65, April1998, which pages are hereby incorporated by reference in theirentirety. For example, grooves in the micron to sub micron range may beobtained. Large dimensions in the mm range may also be obtained withrelative ease. In this way, the silicone lining serves as the “moldingpattern.” However, in some variations, the mold may be patterned with acomplementary groove design. In this way, the mold and the lining, orthe mold itself, may be used to produce the CMP pad groove designs.

FIG. 2 provides a cross-sectional view of an illustrative silicone linedmold (200) as described herein. Shown there, is upper mold plate (202),lower mold plate (204) and silicone lining (206). The silicone lining(206) has embossed or etched patterns (208) therein. It should beunderstood that while the silicone lining (206) is depicted in FIG. 2along the upper mold plate (202), it need not be. Indeed, the siliconelining (206) may also be adhered to, or otherwise retained in, the lowermold plate (204). The silicone lining may be adhered to, or retained inthe mold plate using an suitable method. For example, the siliconelining may be glued, taped, clamped, pressure fit, or otherwise adheredto, or retained in, the mold plate.

Using this method, the CMP pad can be formed from a thermoplastic or athermoset material, or the like. In the case of a thermoplasticmaterial, a melt is typically formed and injected into the siliconelined mold. In the case of a thermoset material, a reactive mixture istypically fed into the silicone lined mold. The reactive mixture may beadded to the mold in one step, or two steps, or more. However,irrespective of the material used, the pad is typically allowed toattain its final shape by letting the pad material cure, cool down, orotherwise set up as a solid, before being taken out of the mold. In onevariation, the material is polyurethane, and polyurethane pads areproduced. For example, a polyurethane pellet may be melted and placedinto the silicone lined mold. The silicone lined mold is etched with thedesired pad pattern as described above. The polyurethane is allowed tocool, and is then taken out of the mold. The pad then has patternscorresponding to those of the silicone lined mold.

The potential advantages of producing in-situ grooves using thissilicone lining method are several. For example, it may provide for alonger life of the mold because the silicone lining can be replacedeasily if it breaks or if there is any wear or tear, and the siliconelining itself typically has a very long lifetime. Similarly, it iseasier to remove the pad from the silicone lined mold as compared to amold where the patterns are engraved therein. Hence, grooves producedusing silicone lined molds may be more accurate, and damage to the padsduring removal may be minimized. In a like manner, the groove sizesproduced using silicone lined molds may be better controlled and betterdefined. For example, very small dimensions (e.g., lateral andhorizontal grooves in the micron to submicron ranges) maybe achieved.Better control and better definition of groove dimensions may be ofparticular interest in pads for specialized purposes such as low-Kdielectrics, Cu removal, STI, SoC, and the like.

Novel Groove Designs

Novel groove designs are also described here. These novel groove designswere largely developed based on flow visualization studies. Thesestudies helped to identify the flow patterns of the slurry on top of thepads. In this way, desirable trajectories of the grooves werecalculated. At smaller radius values (i.e., near the inner portion ofthe pads), grooves were designed with concentric circular grooves tofollow the identified flow patterns. At higher radius values (i.e., nearthe outer portion of the pads), grooves were designed to curtail theflow, e.g., by designing tangential grooves and removing the concentriccircular grooves. Typical groove widths range from about 50 to about 500microns, while typical groove depth ranges from about 100 to about 1000microns.

FIGS. 3A-3I provide illustrations of suitable groove designs asdescribed herein. For example, shown in FIG. 3A is a CMP pad havingreverse logarithmic grooves. FIG. 3B provides another depiction of anovel groove design where the grooves are overlapping circular grooves.While the grooves depicted in FIG. 3B are off-center, they need not be.FIG. 3C provides an illustration of a novel groove design where thedesign comprises double spiral grooves. FIG. 3D depicts a lassajousgroove design, and FIGS. 3E to FIG. 3G depict variations havingconcentric circular grooves and axially grooves. As shown there, in somevariations, the concentric circular grooves are spaced apart in sets, asin FIG. 3G. Similarly, in some variations, the axially curved groovesare overlapping as depicted in FIGS. 3F and 3G.

FIG. 3H shows a design having multiply overlapping axially curvedgrooves. This design may be particularly useful for soft polishing. FIG.3I shows yet another design comprising concentric circular grooves andaxially curved grooves, wherein the axially curved grooves arediscontinuous. This variation may be particularly useful for reducingslurry loss.

These novel groove designs may be produced by any suitable method. Forexample, they may be produced using the in-situ methods described above,or they may be produced using ex-situ or mechanical methods, such aslaser writing or cutting, water jet cutting, 3-D printing, thermoformingand vacuum forming, micro-contact forming, hot stamping or printing, andthe like. The pads may also be sized or scaled as practicable to anysuitable or desirable dimension. As described above, typically thescaling of the pads is based upon the size of the wafer to be polished.Illustrative dimensions were described above.

A. Laser Writing (Laser Cutting)

Laser writing or cutting may be used to make the novel groove designsdescribed herein. Laser cutters typically consist of a downward-facinglaser, which is mounted on a mechanically controlled positioningmechanism. A sheet of material, e.g., plastic, is placed under theworking area of the laser mechanism. As the laser sweeps back and forthover the pad surface, the laser vaporizes the material forming a smallchannel or cavity at the spot in which the laser hits the surface. Theresulting grooves/cuts are typically accurate and precise, and requireno surface finishing. Typically, grooving of any pattern may beprogrammed into the laser cutting machine. More information on laserwriting may be found in J. Kim et al, J. Laser Applications, vol. 15(4),pp 255-260, November 2003, which pages are hereby incorporated byreference in their entirety.

B. Water Jet Cutting

Water jet cutting may also be used to produce the novel groove designsdescribed herein. This process uses a jet of pressurized water (e.g., ashigh as 60,000 pounds per square inch) to make grooves in the pad.Often, the water is mixed with an abrasive like garnet, whichfacilitates better tolerances, and good edge finishing. In order toachieve grooving of a desired pattern, the waterjet is typicallypre-programmed (e.g., using a computer) to follow desired geometricalpath. Additional description of water jet cutting may be found in J. P.Duarte et al, Abrasive water jet, Rivista De Metalurgica, vol. 34(2), pp217-219, March-April 1998, which pages are hereby incorporated byreference in their entirety.

C. 3-D Printing

Three Dimensional printing (or 3-D printing) is another process that maybe used to produce the novel groove designs described here. In 3-Dprinting, parts are built in layers. A computer (CAD) model of therequired part is first made and then a slicing algorithm maps theinformation for every layer. Every layer starts off with a thindistribution of powder spread over the surface of a powder bed. A chosenbinder material then selectively joins particles where the object is tobe formed. Then a piston which supports the powder bed and thepart-in-progress is lowered in order for the next powder layer to beformed. After each layer, the same process is repeated followed by afinal heat treatment to make the part. Since 3-D printing can exerciselocal control over the material composition, microstructure, and surfacetexture, many new (and previously inaccessible) groove geometries may beachieved with this method. More information on 3-D printing may be foundin Anon et al, 3-D printing speeds prototype dev., Molding Systems, vol.56(5), pp 40-41, 1998, which pages are hereby incorporated by referencein their entirety.

D. Thermoforming and Vacuum Forming

Other processes that may be used to produce the novel groove designsdescribed here are thermoforming and vacuum forming. Typically, theseprocesses only work for thermoplastic materials. In thermoforming, aflat sheet of plastic is brought in contact with a mold after heatingusing vacuum pressure or mechanical pressure. Thermoforming techniquestypically produce pads having good tolerances, tight specifications, andsharp details in groove design. Indeed, thermoformed pads are usuallycomparable to, and sometimes even better in quality than, injectionmolded pieces, while costing much less. More information onthermoforming may be found in M. Heckele et al., Rev. on micro moldingof thermoplastic polymers, J. micromechanics and microengineering, vol.14(3), pp R1-R14, March 2004, which pages are hereby incorporated byreference in their entirety.

Vacuum forming molds sheet plastic into a desired shape through vacuumsuction of the warmed plastic onto a mold. Vacuum forming may be used tomold a specific thicknesses of plastic, for example 5 mm. Fairly complexmoldings, and hence complex groove patterns, may be achieved with vacuummolding with relative ease.

E. Micro-contact Printing

Using micro contact printing (μCP), which is a high-resolution printingtechnique grooves can be embossed/printed on top of a CMP pad. This issometimes characterized as “Soft Lithography.” This method uses anelastomeric stamp to transfer a pattern onto the CMP pad. This method isa convenient, low-cost, non-photolithographic method for the formationand manufacturing of microstructures that can be used as grooves. Thesemethods may be used to generate patterns and structures having featuresizes in the nanometer and micrometer (e.g., 0.1 to 1 micron) range.

F. Hot Stamping, Printing

Hot stamping can be used to generate the novel grooves designs describehere as well. In this process, a thermoplastic polymer may be hotembossed using a hard master (e.g., a piece of metal or other materialthat has a pattern embossed in it, can withstand elevated temperatures,and has sufficient rigidity to allow the polymer pad to become embossedwhen pressed into the hard master.) When the polymer is heated to aviscous state, it may be shaped under pressure. After conforming to theshape of the stamp, it may be hardened by cooling below the glasstransition temperature. Grooving patterns of different types may beachieved by varying the initial pattern on the master stamp. Inaddition, this method allows for the generation of nanostructures, whichmay be replicated on large surfaces using molding of thermoplasticmaterials (e.g., by making a stamp with a nano-relief structure). Such anano-structure may be used to provide local grading/grooving on thesematerials that may be useful for several CMP processes. W. Spalte,Hot-stamping for surface-treatment of plastics, Kunsstoffe-GermanPlastics, vol. 76(12), pp 1196-1199, December 1986, which pages arehereby incorporated by reference in their entirety, provides moreinformation on hot stamping.

1. A CMP pad comprising: concentric circular grooves in a first regionof the pad and in a second region of the pad adjacent to the firstregion and radiating grooves which radiate linearly in the first regionof the pad and are curved in the second region of the pad, wherein theradiating grooves cross the concentric circular grooves and wherein thefirst region is closer than the second region, to a central axis of thepad.
 2. The CMP pad of claim 1 wherein the CMP pad is made frompolyurethane.
 3. The CMP pad of claim 1 wherein the grooves are producedby a method from the group consisting of silicone lining, laser writing,water jet cuffing, 3-D printing, thermoforming, vacuum forming,micro-contact printing, hot stamping, and mixtures thereof.
 4. The CMPpad of claim 1 wherein the radiating grooves are continuous.
 5. The CMPpad of claim 4 wherein the CMP pad is made from polyurethane.
 6. The CMPpad of claim 5 wherein the circular grooves occupy a majority of asurface of the pad.
 7. The CMP pad of claim 6 wherein the radiatinggrooves traverse a majority of the surface.